Can I prevent XP from modifying Vista files?

I have vista operating on one hard disk and xp professional running on a small partition of another. I use the larger partition on the second hard disk as the location for vista's "my documents" folder and other media that I would like to be shared between the two operating systems. However, while I want XP to be able to run programs from Vista's hard disk, I don't want it to be able to modify them... I don't want a user in XP being able to delete my Vista utilities and security programs.

Is it possible to disallow XP to modify files in a certain disk or partition?

 

I don't know, but if I were you I would just get rid of XP and get Vista for the whole drive.

 

I wonder if there is such a device like a KVM for hard drives? Unless you wanted to go about it strictly software, though by the sounds of your setup, nothing scares you.

EDIT:
You could have the Vista HDD set to the same letter as the XP HDD and then to access files and programs by paths through cmd, unless that as well goes with the letter convention. I'm sure if that works no average user could figure that one out.